The present invention relates generally to gaseous sterilization and biocidal reduction processes of the type in which volatile gases such as alkylene oxides, are used as biocidal agents to reduce the concentration of viable organisms present as contaminants on and in articles in which such presence is objectionable. Gaseous sterilization and biocidal reduction with gaseous agents including ethylene oxide and propylene oxide are widely accepted techniques specially adapted to the treatment of perishable and fragile substances such as agricultural products, foodstuffs, pharmaceutical agents and medical and surgical instruments and apparatus, including ingredients instruments, devices and apparatus treated in hospital-type gaseous sterilizers.
Alkylene oxides such as ethylene oxide or propylene oxide gases have been employed extensively in the sterilization and biocidal reduction of many types of materials because of the non-corrosive nature of the gases and because the gases are nondestructive with respect to most materials including plastics, adhesives, commestibles, drugs, and delicate equipment including delicate metallic devices. An additional attractive feature of these gases is that they are highly effective biocidal materials at ambient temperatures and that they act rapidly.
However, the use of gases such as alkylene oxides as biocidal or sterilizing agents is subject to several objections, for example, a high degree of flammability. Additionally, mixtures of the lower alkylene oxides such as ethylene oxide and propylene oxide with air, in certain proportions, are explosive. In order to reduce or substantially to eliminate the hazards indicated, it has been a common practice to dilute alkylene oxides with inert gases such as halogenated hydrocarbons or with carbon dioxide. A commercially available mixture consists of about 12% by weight of ethylene oxide mixed with about 88% by weight of a halogenated hydrocarbon such as dichloro difluoro methane (Freon 12) to obviate flammability and to prevent formation of an explosive atmosphere.
The conventional manner in which the biocidal gas system is used is to place articles or materials in a reactor tank or chamber and then to introduce a predetermined composition of biocidal gas at controlled conditions of temperature and pressure. Upon the elapse of a predetermined treatment period, the biocidal gas is pumped from the reactor and either discarded into the atmosphere; or diluted with water and discarded into the sewers or a dry well; or reclaimed for reconstitution and reuse. The discharge or release of the spent biocidal gas into the atmosphere, sewers or a dry well poses ecological problems. This is also true for biocidal gaseous systems which include the halogenated hydrocarbons as diluents. Moreover, the presence of such diluents has been found to have a deterent effect upon the activity of the biocidal gas itself, so that longer treatment periods have been required in order to ensure effective reduction in the concentration of viable organisms.
The aim of the present invention is to obviate the shortcomings of prior art compositions and techniques and to provide a process and apparatus whereby the spent biocidal gases may be effectively and safely disposed of without hazard and without contaminating the ambient atmosphere with these gases.